Compsci 101, Fall 2012, Transform Nutshell

This is the assignment in a nutshell: what to do and a summary of the ideas needed to do it.

This assignment is about looping over lists, reading and writing files, and using functions to transform data from one form to another. It's also about reading code provided to you and trying to fit new code into the existing code. This is a skill that's needed in writing all kinds of programs. You have to do three things:

Transform a list of lists. Each list is the words on a line of a file read.
Write the transformed words to a file, with each line of the written file containing the transformed words on the line of the corresponding read file.
Add some transforms to apply: piglatin and rot13.

Reading Code

You should look at the code in function tansform_file (see it in FileTransform.py) to see the steps taken when the program is run:

User chooses a file to read.
User chooses a transform to apply to every word in the file read.
User chooses a file to write the transformed words to

You have to write code that accomplishes the last two steps by adding code to the functions transform and write_words respectively. Do these one at a time, working on transform first.

You can test transform by converting words to upper-case.

List of Lists

The file of words that's read is stored in a list. Each element of the list is also a list -- of the words on each line of the file read. The list returned by get_words, stored in variable words in the function transform_file, is this list of lists.

The list words[0] is the first line of the file read, with each word on that line an element of words[0]. Thus to print the second line of the file read, which is stored in words[1] you could use this code (note that the comma keeps the words printed on one line, the print after the loop moves the console-cursor to the next line.

for word in words[1]: print word, print

Writing `transform`

The function transform takes the list of lists and returns a copy, a new list, of transformed words. The parameter lines is the list of lists, e.g., lines[0] is a list of the words on the first line of the file read. The value returned is also a list of lists, e.g., with copy[0] being the list of words on the first line that have been transformed.

This means if lines[0] is ["The", "big", "dog", "barked"] then copy[0] would be ["THE", "BIG", "DOG", "BARKED"] if the uppercase transform is chosen.

The second parameter to the function transform is actually the function to apply to each word -- instead of passing a list, a string, or an int --- the code passes a function like transform_upper or transform_pig. This parameter is named func -- to apply it you could write this list comprehension, for example, to every word in copy[index]

tform = [func(w) for w in copy[index]] This creates a list of words, each word having been transformed by the call func(w) -- remember that func is actually something like transform_pig.

Writing `write_words`

The function you're given prints to a console. You have to modify it to write to a file. The file is a parameter to the function (the name of the parameter is file --- this is a bad name as we discussed in class because it's a type in Python).

The code you're given prints every word, a space after every word, and puts the words on a line from the file on a line of the console. You need to call file.write appropriately to mirror what's done on the console: words, spaces, and newlines.

Writing Transforms

Use the APTs for piglatin and rot13 to help get these correct. Add functions to do the transforms to the beginning of the code in FileTransform.py and be sure to add the function name for rot13 to the list of functions choose_transform.